Blood cells are produced in bone marrow, differentiated from immature cells to mature cells and migrated into peripheral blood. In healthy subject, immature leukocytes do not appear in peripheral blood. However, in some cases, immature leukocytes appear in peripheral blood of patients suffering from leukemia, cancer metastasis to the bone marrow, multiple myeloma, severe infection or the like. Therefore, it is very important to classify and measure mature and immature leukocytes in biological samples in order to diagnose these diseases.
A reagent disclosed in Japanese Unexamined Patent Publication No. Hei 10 (1998)-206423 is known as a reagent for measuring immature leukocytes. This reagent is mixed with a biological sample to form a measurement sample, the obtained measurement sample is introduced into a flow cytometer and mature and immature leukocytes in the sample are classified and respectively counted based on optical information obtained by applying light having a specific wave length. Further, immature leukocytes can be further classified into myeloblasts, immature granulocytes and the like and they can be measured respectively.